/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */

/*
 * This package is based on the work done by Timothy Gerard Endres
 * (time@ice.com) to whom the Ant project is very grateful for his great code.
 */

package org.apache.tools.tar;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;

/**
 * The TarBuffer class implements the tar archive concept of a buffered input stream. This concept goes back to the days
 * of blocked tape drives and special io devices. In the Java universe, the only real function that this class performs
 * is to ensure that files have the correct "block" size, or other tars will complain.
 * <p>
 * You should never have a need to access this class directly. TarBuffers are created by Tar IO Streams.
 */

public class TarBuffer{

    /** Default record size */
    public static final int DEFAULT_RCDSIZE = 512;

    /** Default block size */
    public static final int DEFAULT_BLKSIZE = DEFAULT_RCDSIZE * 20;

    private InputStream     inStream;
    private OutputStream    outStream;
    private byte[]          blockBuffer;
    private int             currBlkIdx;
    private int             currRecIdx;
    private int             blockSize;
    private int             recordSize;
    private int             recsPerBlock;
    private boolean         debug;

    /**
     * Constructor for a TarBuffer on an input stream.
     * 
     * @param inStream
     *            the input stream to use
     */
    public TarBuffer(InputStream inStream){
        this(inStream, TarBuffer.DEFAULT_BLKSIZE);
    }

    /**
     * Constructor for a TarBuffer on an input stream.
     * 
     * @param inStream
     *            the input stream to use
     * @param blockSize
     *            the block size to use
     */
    public TarBuffer(InputStream inStream, int blockSize){
        this(inStream, blockSize, TarBuffer.DEFAULT_RCDSIZE);
    }

    /**
     * Constructor for a TarBuffer on an input stream.
     * 
     * @param inStream
     *            the input stream to use
     * @param blockSize
     *            the block size to use
     * @param recordSize
     *            the record size to use
     */
    public TarBuffer(InputStream inStream, int blockSize, int recordSize){
        this.inStream = inStream;
        outStream = null;

        initialize(blockSize, recordSize);
    }

    /**
     * Constructor for a TarBuffer on an output stream.
     * 
     * @param outStream
     *            the output stream to use
     */
    public TarBuffer(OutputStream outStream){
        this(outStream, TarBuffer.DEFAULT_BLKSIZE);
    }

    /**
     * Constructor for a TarBuffer on an output stream.
     * 
     * @param outStream
     *            the output stream to use
     * @param blockSize
     *            the block size to use
     */
    public TarBuffer(OutputStream outStream, int blockSize){
        this(outStream, blockSize, TarBuffer.DEFAULT_RCDSIZE);
    }

    /**
     * Constructor for a TarBuffer on an output stream.
     * 
     * @param outStream
     *            the output stream to use
     * @param blockSize
     *            the block size to use
     * @param recordSize
     *            the record size to use
     */
    public TarBuffer(OutputStream outStream, int blockSize, int recordSize){
        inStream = null;
        this.outStream = outStream;

        initialize(blockSize, recordSize);
    }

    /**
     * Initialization common to all constructors.
     */
    private void initialize(int blockSize, int recordSize){
        debug = false;
        this.blockSize = blockSize;
        this.recordSize = recordSize;
        recsPerBlock = this.blockSize / this.recordSize;
        blockBuffer = new byte[this.blockSize];

        if(inStream != null){
            currBlkIdx = -1;
            currRecIdx = recsPerBlock;
        }else{
            currBlkIdx = 0;
            currRecIdx = 0;
        }
    }

    /**
     * Get the TAR Buffer's block size. Blocks consist of multiple records.
     * 
     * @return the block size
     */
    public int getBlockSize(){
        return blockSize;
    }

    /**
     * Get the TAR Buffer's record size.
     * 
     * @return the record size
     */
    public int getRecordSize(){
        return recordSize;
    }

    /**
     * Set the debugging flag for the buffer.
     * 
     * @param debug
     *            If true, print debugging output.
     */
    public void setDebug(boolean debug){
        this.debug = debug;
    }

    /**
     * Determine if an archive record indicate End of Archive. End of archive is indicated by a record that consists
     * entirely of null bytes.
     * 
     * @param record
     *            The record data to check.
     * @return true if the record data is an End of Archive
     */
    public boolean isEOFRecord(byte[] record){
        for(int i = 0, sz = getRecordSize(); i < sz; ++i){
            if(record[i] != 0){
                return false;
            }
        }

        return true;
    }

    /**
     * Skip over a record on the input stream.
     * 
     * @throws IOException
     *             on error
     */
    public void skipRecord() throws IOException{
        if(debug){
            System.err.println("SkipRecord: recIdx = " + currRecIdx
                + " blkIdx = " + currBlkIdx);
        }

        if(inStream == null){
            throw new IOException("reading (via skip) from an output buffer");
        }

        if(currRecIdx >= recsPerBlock){
            if(!readBlock()){
                return; // UNDONE
            }
        }

        currRecIdx++;
    }

    /**
     * Read a record from the input stream and return the data.
     * 
     * @return The record data.
     * @throws IOException
     *             on error
     */
    public byte[] readRecord() throws IOException{
        if(debug){
            System.err.println("ReadRecord: recIdx = " + currRecIdx
                + " blkIdx = " + currBlkIdx);
        }

        if(inStream == null){
            throw new IOException("reading from an output buffer");
        }

        if(currRecIdx >= recsPerBlock){
            if(!readBlock()){
                return null;
            }
        }

        byte[] result = new byte[recordSize];

        System.arraycopy(blockBuffer, (currRecIdx * recordSize), result, 0,
            recordSize);

        currRecIdx++;

        return result;
    }

    /**
     * @return false if End-Of-File, else true
     */
    private boolean readBlock() throws IOException{
        if(debug){
            System.err.println("ReadBlock: blkIdx = " + currBlkIdx);
        }

        if(inStream == null){
            throw new IOException("reading from an output buffer");
        }

        currRecIdx = 0;

        int offset = 0;
        int bytesNeeded = blockSize;

        while(bytesNeeded > 0){
            long numBytes = inStream.read(blockBuffer, offset, bytesNeeded);

            //
            // NOTE
            // We have fit EOF, and the block is not full!
            //
            // This is a broken archive. It does not follow the standard
            // blocking algorithm. However, because we are generous, and
            // it requires little effort, we will simply ignore the error
            // and continue as if the entire block were read. This does
            // not appear to break anything upstream. We used to return
            // false in this case.
            //
            // Thanks to 'Yohann.Roussel@alcatel.fr' for this fix.
            //
            if(numBytes == -1){
                if(offset == 0){
                    // Ensure that we do not read gigabytes of zeros
                    // for a corrupt tar file.
                    // See http://issues.apache.org/bugzilla/show_bug.cgi?id=39924
                    return false;
                }
                // However, just leaving the unread portion of the buffer dirty does
                // cause problems in some cases.  This problem is described in
                // http://issues.apache.org/bugzilla/show_bug.cgi?id=29877
                //
                // The solution is to fill the unused portion of the buffer with zeros.

                Arrays.fill(blockBuffer, offset, offset + bytesNeeded, (byte)0);

                break;
            }

            offset += numBytes;
            bytesNeeded -= numBytes;

            if(numBytes != blockSize){
                if(debug){
                    System.err.println("ReadBlock: INCOMPLETE READ " + numBytes
                        + " of " + blockSize + " bytes read.");
                }
            }
        }

        currBlkIdx++;

        return true;
    }

    /**
     * Get the current block number, zero based.
     * 
     * @return The current zero based block number.
     */
    public int getCurrentBlockNum(){
        return currBlkIdx;
    }

    /**
     * Get the current record number, within the current block, zero based. Thus, current offset = (currentBlockNum *
     * recsPerBlk) + currentRecNum.
     * 
     * @return The current zero based record number.
     */
    public int getCurrentRecordNum(){
        return currRecIdx - 1;
    }

    /**
     * Write an archive record to the archive.
     * 
     * @param record
     *            The record data to write to the archive.
     * @throws IOException
     *             on error
     */
    public void writeRecord(byte[] record) throws IOException{
        if(debug){
            System.err.println("WriteRecord: recIdx = " + currRecIdx
                + " blkIdx = " + currBlkIdx);
        }

        if(outStream == null){
            throw new IOException("writing to an input buffer");
        }

        if(record.length != recordSize){
            throw new IOException("record to write has length '"
                + record.length + "' which is not the record size of '"
                + recordSize + "'");
        }

        if(currRecIdx >= recsPerBlock){
            writeBlock();
        }

        System.arraycopy(record, 0, blockBuffer, (currRecIdx * recordSize),
            recordSize);

        currRecIdx++;
    }

    /**
     * Write an archive record to the archive, where the record may be inside of a larger array buffer. The buffer must
     * be "offset plus record size" long.
     * 
     * @param buf
     *            The buffer containing the record data to write.
     * @param offset
     *            The offset of the record data within buf.
     * @throws IOException
     *             on error
     */
    public void writeRecord(byte[] buf, int offset) throws IOException{
        if(debug){
            System.err.println("WriteRecord: recIdx = " + currRecIdx
                + " blkIdx = " + currBlkIdx);
        }

        if(outStream == null){
            throw new IOException("writing to an input buffer");
        }

        if(offset + recordSize > buf.length){
            throw new IOException("record has length '" + buf.length
                + "' with offset '" + offset
                + "' which is less than the record size of '" + recordSize
                + "'");
        }

        if(currRecIdx >= recsPerBlock){
            writeBlock();
        }

        System.arraycopy(buf, offset, blockBuffer, (currRecIdx * recordSize),
            recordSize);

        currRecIdx++;
    }

    /**
     * Write a TarBuffer block to the archive.
     */
    private void writeBlock() throws IOException{
        if(debug){
            System.err.println("WriteBlock: blkIdx = " + currBlkIdx);
        }

        if(outStream == null){
            throw new IOException("writing to an input buffer");
        }

        outStream.write(blockBuffer, 0, blockSize);
        outStream.flush();

        currRecIdx = 0;
        currBlkIdx++;
    }

    /**
     * Flush the current data block if it has any data in it.
     */
    private void flushBlock() throws IOException{
        if(debug){
            System.err.println("TarBuffer.flushBlock() called.");
        }

        if(outStream == null){
            throw new IOException("writing to an input buffer");
        }

        if(currRecIdx > 0){
            writeBlock();
        }
    }

    /**
     * Close the TarBuffer. If this is an output buffer, also flush the current block before closing.
     * 
     * @throws IOException
     *             on error
     */
    public void close() throws IOException{
        if(debug){
            System.err.println("TarBuffer.closeBuffer().");
        }

        if(outStream != null){
            flushBlock();

            if(outStream != System.out && outStream != System.err){
                outStream.close();

                outStream = null;
            }
        }else if(inStream != null){
            if(inStream != System.in){
                inStream.close();

                inStream = null;
            }
        }
    }
}
